Continuous electroplating method



Filed May 231, 1962 CLEANSING s. momma PLAYING I PLATING SDLUTIOM sumv52 48 H METAL cnmmm ROLL 44) n W RUBBER WW coma max up 6% 50 pcARsommom; 43 R SUPPORT mums 54 CURRENT sounce,so 70 L AMP HOUR ALARM METER 6458 INVENTUEt A. FOREST WELLS Hfififi A TTOR IV E Yd" United StatesPatent 3,264,198 CONTINUOUS ELECTROPLATIN G METHOD Arthur Forest Wells,Chesterton, Ind., assignor to Nation- 21 Steel Corporation, acorporation of Delaware Filed May 31, 1962, Ser. No. 199,051 2 Claims.(Cl. 204-28) This invention is concerned with methods and apparatus forobtaining improved uniformity in the electroplating of a continuouslymoving base metal.

In continuous electroplating, the material to be plated is passed inimmediate succession through a series of plating cells and the desiredcoating weight is built up progressively in each cell. Some of the mainobjectives of continuous electroplating operations are accurate controlof coating weight and uniformity of the coating. To a large degree bothof these objectives are dependent on maintaining uniform spacing betweenthe anode (plating metal) and the cathode (base metal) in each cell. Theimportance of uniform spacing between the anode and cathode isaccentuated in plating continuous strip since it is desired to havecoating weight and appearance uniform across the entire width of thestrip. Also, the continuous nature of these operations adds difiicultiesnot found in batch processing for example. The continuous operationcannot be interrupted to measure or adjust the anode position or tochange anodes. Further, plating characteristics affecting anode erosiondiffer from cell to cell and anode erosion differs with differingcoating weights, strip speeds, etc. Prior to the present invention,attempts were made to calculate erosion time for an anode so thatuniform spacing between anode and cathode could be maintained. Becauseof the different characteristics of each cell and the effects ofchanging coating weights, changing line speeds, variations in thecurrent source, etc., it was impossible to calculate anode erosion withany accuracy. With some calculation, trial and error, and a good deal ofexperience the operator could attempt to guess the proper time to changeanode bars in a continuou operation. With the teachings of thisinvention these problems are eliminated since the above mentionedvariables affecting anode erosion are automatically integrated and aprecise measurement is made which accurately indicates the proper timeto change anode bars in each cell of a continuous electroplating line.

The invention will be described in relation to a Halogen Process linefor continuous electro-tinplating of steel strip although its teachingsare applicable to other continuous operations using other plating metalsand other base metals.

In the drawings:

FIGURE 1 is a schematic diagram of a continuous tinplating line of theHalogen type;

FIGURE 2 is a schematic diagram of a plating cell embodying theinvention; and

FIGURE 3 is a sectional view of a portion of FIG- URE 2 taken along theline 3-3.

Refer-ring to FIGURE 1, coils of steel strip are formed into continuousstrip at uncoilers and fed through looping pit 12 and cleansing andpickling means 14 preparatory to plating. In the Halogen Process, thestrip is plated on one surface at a time, first in a series of platingcells in plating tier 16, then after inversion of the strip by rolls 18and 20, on the opposite surface in a second tier of plating cells 22.Solution recovery and wash rinses are provided at 26 in a third tierabove the plating cell tiers 16 and 22. Thereafter the strip is passedthrough a fusion tower 28 where the plated tin is brightened by meltingand subsequent quenching. After passage through looping pit 30- thefinished strip is formed into coils or may be sheared into desiredlengths. 1

In a Halogen type line each plating tier may contain twelve, sixteen, ormore, plating cells and the strip passes in immediate succession fromone cell to the next. The speed of the line may vary up to about 2100feet per minute, or more. Under these conditions it is essential toaccurately control plating in each cell. Further, uniform plating acrossthe full width of the strip requires that 'the distance between the tinanode and the steel strip cathode be kept uniform across the full widthof the strip. Since the operation is continuous, the line cannot bestopped to change anodes; therefore the anode is in the form of barsdisposed side by side on guides so that they can be moved progressivelyacross the line of travel of the strip. Referring to FIGURES 2 and 3,anode bars 40 are shown supported on anode support bar 42 and tankguides 43. Anode bars 40 extend across the full width of strip 44 andthe distance separating the anode bars 40 and strip 44 is kept uniformby moving the bars along the inclined plane provided by the anodesupport bar 42 and guides 43. As the anode bars erode they are movedprogressively up the inclined plane by periodically removing theuppermost anode bar and adding a bar at the opposite end of the inclinedplane.

Ordinarily it is not possible to see the anode bars because of the strip44 and the near opacity of plating solution 46; nor is it convenientlypossible to physically measure the distance between the anode 40 and thestrip 44. As previously indicated, changing of anode bars has been basedlargely on a matter of experience. The skill required was of the highestorder and, considering the complexity of the problem stemming fromchanging coating weights during production runs, changing line speeds,differing resistances in the various plating cells, etc., precision wasnot to be expected and seldom obtained. The problems are similar invertically oriented continuous electroplating lines and the inventionsimilarly provides methods and apparatus for accurately determining whenan anode bar should be changed in such lines with improved coatingcontrol and uniformity similarly resulting.

Referringin particular to FIGURE 2, strip 44 passes between contact roll48 and backup roll 50 onto plating cell 52. A continuous electroplatingline includes a plurality of substantially identical plating cells, suchas that shown schematically in FIGURE 2, arranged in immediatesuccession. Strip 44 is 'the cathode in each cell and electrical contactis completed through a metal contact roll such as cathode contact roll48. For purposes of explanation, the plating circuit of cell 52 can beconsidered as including plating current source 60, anode conductor 55,anode support 42, anode means 40, plating solution 46, strip (cathode)44, and cathode contact roll 48. Plating current source 60 is joined tocathode contact roll 48 by connector 62 and to anode conductor 55 byconnector 64.

In accordance with the teachings of the invention, a quantitativemeasurement of the electricity delivered to the plating solution 46 byanode 40 is made and this measurement provides a quantitativemeasurement of the amount of anode 40 which has entered into thesolution. To effect such quantitative measurements, impedance 66 isconnected in the plating circuit to serve as a meter shunt. Ampere hourmeter 68 is connected across the shunt represented by impedance 66.Ampere hour meter 68 is an integrating meter which sums up the currentin the plating circuit with respect to time. In this way the anodeerosion effects of the variables which are nearly impossible tocalculate or estimate, such as changing line speeds, changing coatingthicknesses, differing plating efiiciencies in the various cells, etc.,are taken into account 3 by ampere meter 68 and a single output producedfor each cell which totalizes these effects. Dial 70 of ampere hourmeter 68 can be calibrated to read directly in ampere hours or in anodeerosion so that a reading from ampere hour meter 68 can be used toindicate when an anode bar should be changed. Ampere hour meter 68 canalso be utilized to actuate a visual and/ or audio alarm 72 to indicatewhen an anode bar should be changed. The operation of an ampere hourmeter is well known in the art and no further description of theinstrument itself is necessary to an understanding of the invention. Asuitable ampere hour meter for continuous electro-tinplating operationavailable on the market is the Standard D.C. Sangamo Ampere Hour Meter#9518234, ampere rating 12,000 amperes.

In the specific embodiment described, a Halogen Process line, tin isplated from its bivalent ion. Each plating tier includes sixteen platingcells. The anode in each cell includes two banks of anode bars withsixteen bars in each bank. The anode bars weigh approximately ninetypounds apiece when added to a cell after the line is in operation. Atthe start of a new line, anode bars are cast in special molds with theweight of each anode bar varying with its position in the bank. In thisway the parallel relationship between the strip and the top surfaces ofthe anode bars is obtained initially. After the line is in stabilizedoperation this parallel relation is maintained by periodically removingthe uppermost bar in each bank and adding a bar to each bank at thelower end of the inclined plane formed by the anode support and guides.Anode bars when removed Weigh approximately twenty-nine pounds. Anampere hour meter is connected at each plating cell and a total oftwenty-five thousand ampere hours is required between changes of anodebars. The anode efliciency of these plating cells is held constant atabout 100% so that a total of approximately one hundred and twenty-twopounds of tin is plated out by the twenty-five thousand ampere hours.From these figures, those skilled in the art will be able to calculatethe required number of ampere hours between anode bar changes for othertypes of electro-tinplating lines or lines for electroplating othertypes of metals.

In this description the anode means has been designated as electricallypositive and the cathode means as electrically negative. Thisnomenclature is in accordance with electrical theory which considerscurrent flow to be from positive to negative in circuit analysis. Inelectrical theory which considers electron flow to be from negative topositive, the polarity designation or electrode names could be reversed.Therefore, for purposes of defining the invention in the claims, theterm anode refers to the element providing plating metal and cathode tothe element being plated, without limitation to the polarity or otherdesignation employed in practice. The invention has been described withparticular reference to a continuous'electro-tinplating line of theHalogen Process type. Further details of this type of line can be foundin Apparatus for Electrocoating Striplike Material, Reissue Patent23,456 to E. W. Rieger, issued January 22, 1952 or 4 in ElectrotinningSteel Strip, Metal Finishing, February 1944, pages 77-79, both of whichare incorporated herein by reference.

While the invention has been described with particular 5 reference to aline for plating continuous steel strip, the teachings of the inventionare applicable to the plating of other elongated, continuously moving,metallic materials; reference being bad to the appended claims fordefining the limits of the invention.

What is claimed is:

1. Continuous strip electroplating process in which plating metal supplyis continuously maintained within a plating cell comprising the steps ofpassing continuous strip longitudinally through a plating cell having ananode made up of a plurality of individual elongated anode elementsarranged in side by side relationship with predetermined spacing betweenthe anode elements and the continuous strip across its full width,

supplying plating current to the plating cell,

quantitatively measuring plating current delivered to the cell as ameasure of anode erosion, and

adding a new anode element to the cell and progressively movingpartially eroded anode elements in a direction across the width of thecontinuous strip responsive to the quantitative measurement of platingcurrent delivered to the cell to maintain the predetermined spacingbetween the anode elements and the continuous strip.

2. Continuous steel strip electroplating process in which plating metalsupply is continuously maintained within a plating cell comprising thesteps of passing continuous steel strip longitudinally through a platingcell having an anode made up of a plurality of individual elongatedanode elements arranged in side by side relationship with predeterminedspacing between the anode elements and the continuous strip across itsfull width,

supplying plating current to the plating cell,

4 quantitatively measuring the plating current delivered to the cell asa measure of anode erosion, and

adding a new anode element to the plating cell and progressively movingpartially eroded anode elements in a direction across the width of thecontinuous steel strip responsive to the quantitative measurement ofplating current delivered to the cell to maintain the predeterminedspacing between the anode elements and the continuous steel strip.

References Cited by the Examiner UNITED STATES PATENTS 1,527,095 2/1925Turnock 204-228 2,462,506 2/ 1949 Klein 204-225 WINSTON A. DOUGLAS,Primary Examiner. JOHN R. SPECK, JOHN H. MACK, Examiners. R. GOOCH, T.TUFARIELLO, Assistant Examiners.

1. CONTINUOUS STRIP ELECTROPLATING PROCESS IN WHICH PLATING METAL SUPPLYIS CONTINUOUSLY MAINTAINED WITHIN A PLATING CELL COMPRISING THE STEPS OFPASSING CONTINUOUS STRIP LONGITUDINALLY THROUGH A PLATING CELL HAVING ANANODE MADE UP OF A PLURALITY OF INDIVIDUAL ELONGATED ANODE ELEMENTSARRANGED IN SIDE BY SIDE RELATIONSHIP WITH PREDETERMINED SPACING BETWEENTHE ANODE ELEMENTS AND THE CONTINUOUS STRIP ACROSS ITS FULL WIDTH,SUPPLYING PLATING CURRENT TO THE PLATING CELL, QUANTITATIVELY MEASURINGPLATING CURRENT DELIVERED TO THE CELL AS A MEASURRE OF ANODE EROSION,AND ADDING A NEW ANODE ELEMENT TO THE CELL AND PROGRESSIVELY MOVINGPARTIALLY ERODED ANODE ELEMENTS IN A DIRECTION ACROSS THE WIDTH OF THECONTINUOUS STRIP RESPONSIVE TO THE QUANTITATIVE MEASUREMENT OF PLATINGCURRENT DELIVERED TO THE CELL TO MAINTAIN THE PREDETERMINED SPACINGBETWEEN THE ANODE ELEMENTS AND THE CONTINUOUS STRIP.